This invention relates to a road image input system for controlling an automotive vehicle by picking up the scene of a road in the direction in which the vehicle is traveling, setting an image processing area on the image of the road scene picked up, and processing data contained in the image processing area.
In order to keep a four-wheel drive vehicle in an appropriate traveling state despite changes in the road surface on which the vehicle is running, a four-wheel drive control system has been proposed in which the vehicle is switched over to a control mode different from that of the simple four-wheel drive traveling mode whenever necessary.
Such a control system is of two different types. One is a part-time four-wheel drive system in which, in accordance with the road surface conditions, a changeover can be made whenever necessary between two-wheel drive in which either the front or rear wheels are driven and four-wheel drive in which both the front and rear wheels are driven.
The other type of control system is a full-time four-wheel drive system having a center differential mechanism for absorbing a difference in turning radius that develops between the front and rear wheels at cornering. In order to make it possible to switch the control mode in accordance with the road surface conditions, this system is provided with a locking mechanism for direct transfer between the front and rear wheels without the intervention of the center differential mechanism. The center differential mechanism is locked when a large driving force is necessary, as at acceleration or during travel on a poor road surface, and unlocked during ordinary travel when a large driving is not required.
In general, control for switching between two- and four-wheel drive in the part-time configuration or for locking the center differential mechanism in the full-time arrangement is a manual operation performed by the driver based on his or her judgment of the road surface conditions. Recently, however, a system has been proposed in which such control is executed automatically by sensing the traveling state of the vehicle and judging the road surface conditions accordingly. A vital factor for achieving safe and stable vehicle travel with such a system is how to sense the conditions of the road surface accurately.
In the arrangement where the changeover is made manually, the driver must constantly scrutinize the road conditions ahead of the vehicle and the manual changeover operation is a troublesome one. With the automatically controlled system, on the other hand, the state of the road surface on which the vehicle is currently traveling can be sensed but not the road surface conditions ahead of the vehicle. Consequently, there are cases where the changeover between two-wheel/four-wheel drive or the locking of the center differential mechanism occurs after the conditions of the road surface have changed. Accordingly, a suitable response to the road surface conditions may be delayed. This can have a detrimental effect upon the safety and stability of vehicle travel.
One expedient that immediately comes to mind for observing road surface conditions ahead of a traveling vehicle is a camera utilizing a well-known CCD. Generally, in the computerized processing of an image obtained from a camera, processing all of the image data available involves an extremely large quantity of data and therefore requires a considerable period of time. Accordingly, processing time can be shortened if the quantity of image data to be processed is reduced by limiting the subject matter to a processing area or "window" set on the image. In most cases, however, such computerized image processing is for processing solely a specific window on the image on the condition that the camera is not moved; once the window has been set at a specific position, no modification is necessary. This means that such a system cannot be directly applied to the control of a vehicle, for in such case the camera would move when the vehicle does. Let us describe this with reference to FIGS. 1A and 1B.
As shown in FIG. 1A, it is necessary that the window be set on a road surface portion of an image in order that the condition of the road surface ahead of the vehicle may be sensed on the basis of image data obtained from a camera mounted on the vehicle. However, since the road surface portion of interest moves to the left and right on the image plane due to curves in the road, there are instances where the window will not be located on the road surface, as shown in FIG. 1B. The condition of the road surface can no longer be sensed correctly at such time. Furthermore, since there is a response delay between detection of the road condition and control to deal with the condition, control is not always performed at the proper timing, namely at the moment the vehicle passes over the portion of the road surface sensed. Moreover, the condition of the road surface outside the window cannot be sensed merely by setting the window at a single position.